The present invention relates to a laser beam projection device and, more particularly, to an arrangement for permitting control and calibration of the orientation of a rotating laser beam.
A number of different laser beam systems have been employed in the past for surveying and construction applications to provide a rotating reference beam of laser light. This reference plane of light permits ready measurement of elevations and grades. Further, earth moving and other construction equipment may be fitted with laser light sensing devices which may be coupled through control systems to effect automatic or semi-automatic control of the equipment.
A laser beam projector typically employs a rotating pentaprism assembly which sweeps the beam in a horizontal plane or a selected tilted plane. Some prior art projectors have included visually readable level vials and manually adjustable screws for orienting the projector in the desired attitude. Such a projector is disadvantageous in that its accuracy is dependent in part upon the skill of the operator in the initial adjustment of the orientation of the projector. Moreover, a subsequent unnoticed disturbance of the device can cause erroneous measurements to be taken.
A projection device having significant advantages over prior art devices is shown in U.S. Pat. No. 4,062,634, issued Dec. 13, 1977, to Rando et al, and assigned to the present invention. The system disclosed in the Rando et al patent is one in which orientation of the laser beam reference plane is accomplished automatically. A support frame for the laser source is pivotally mounted on the base frame of the Rando et al device. The support frame carries electrical sensor vials which sense the orientation of the support frame and provide electrical signals used by a feedback control system. The control system actuates electric motors to move the support frame into a position in which the vials are leveled. The vials are mounted on the support frame in such a manner that their positions may be adjusted by grade motors. When the reference laser plane is to be oriented at an angle to the horizontal, a grade motor is actuated by the operator to tilt the vial with respect to the support frame. The amount of tilt is displayed on a counter also attached to the motor. The feedback control system then reorients the support frame to bring the vial back into its level position, thus tilting the frame by the desired amount.
It will be appreciated that this requires a number of motors to accomplish the orientation of the vials and the support frame, and is relatively complex and expensive. Additionally, initial calibration of the system shown in Rando et al is not as easily accomplished as may be desired.
Accordingly, it is seen that there is a need for an arrangement for use in a laser beam projection device which controls the orientation of a support frame in a simple fashion, and which facilitates calibration of the projection device.